1. Field of the Invention
The invention relates to the field of angioplasty. In particular, the present invention relates to a balloon protector for a dilatation balloon catheter.
2. Description of the Prior Art
Angioplasty has gained wide acceptance in recent years as an efficient and effective method for opening stenoses in the coronary arteries and in other parts of the vascular system. The most widely used form of angioplasty makes use of a dilatation catheter which has an inflatable balloon at its distal end. Using fluoroscopy, the physician guides the catheter through the vascular system until the balloon is positioned across the stenosis. The balloon is then inflated by supplying a fluid under pressure through an inflation lumen to the balloon. The inflation to the balloon causes stretching of the artery and pressing of the lesion into the artery wall to re-establish acceptable blood flow through the artery.
One important characteristic of a dilatation balloon catheter used for angioplasty is its "profile", which is determined by the outer diameter of the distal end portion of the balloon. Considerable effort has been spent in developing low profile dilatation balloon catheters by minimizing the dimensions of the core or inner tube which extends through the balloon to its distal end, and by reducing wall thicknesses, to the extent possible, of the balloon itself.
Another important consideration is the outer diameter of the balloon in its deflated condition. This outer diameter affects the ease and ability of the dilatation catheter to pass through a guide catheter and through the coronary arteries leading to the stenosis to be opened.
In order to reduce the outer diameter of the balloon catheter in its deflated condition, it is common to fold and/or wrap the flaps of the deflated balloon. When inflation fluid is applied to the deflated balloon, it causes the balloon flaps to unwrap so that the balloon can inflate to its full inflated state.
It has been common to use a balloon protector in conjunction with a balloon dilatation catheter. A balloon protector serves two important functions. First, it protects the balloon and the distal tip of the catheter from possible damage during shipping. Second, the balloon protector wraps the balloon tightly in its deflated condition to minimize the outer diameter of the balloon in its deflated state.
A balloon protector is typically applied to the distal end portion of the catheter prior to sterilization of the catheter. The sterilization process typically involves exposing the catheter, with the balloon protector in place, to an elevated temperature for a predetermined time period.
With certain balloon materials, such as polyolefin, the sterilization process will cause the balloon to be "heat set" in the folded or wrapped condition in which it is held by the balloon protector. As a result, when the balloon protector is later removed, the balloon remains in a tightly wrapped condition. This heat set of balloon has a further advantage in that when the balloon is inflated and is then deflated, the application of a negative fluid pressure during deflation will cause the balloon to tend to return to its heat set, tightly-wrapped shape. This greatly facilitates the removal of the catheter after the dilatation procedure has been performed.
As the catheter distal sections (including the balloon) have become smaller, and more fragile, it has become increasing difficult to apply a balloon protector which does not damage the catheter or the balloon and yet wraps the balloon as tightly as possible. There is a continuing need for improved balloon protectors for dilatation balloon catheters.